Biodiversity in Canadian Lakes and Rivers
- Trends in Freshwater Fish of Special Interest
- Trends in Hydrological Regimes
- Trends in River and Lake Ice Break-Up/Freeze-Up
- Trends in Habitat Loss and Fragmentation
- Trends in Pollutants in Lake and River Systems
- Future Climate Impacts on Lakes and Rivers
- Synthesis of Data
- Appendix 1
Trends in Pollutants in Lake and River Systems
Contaminants entering the environment will partition into different environmental compartments (such as water and biota) in a fashion determined by their chemical and physical properties. Since the environment itself is in a state of constant physio-chemical flux, it is not always straightforward to predict by which pathway or in which compartment specific substances will accumulate. For this reason, spatial and temporal interpretation of contaminant monitoring data is often hampered by a lack of sufficient observations, and by other confounding factors such as analytical method inconsistencies (Braune et al., 1999). Moreover, observations within a single system may not easily be generalized to other systems: for example, where food web structure varies between lakes food-chain bioaccumulation of contaminants by top predators will vary according to food chain length and trophic position, even where contaminant levels at the base of the food web are similar (Baird et al., 2001). For this reason, and given the general lack of available time series data within Canada on contaminants, either in terms of water or tissue/biota concentrations (see below), it was not possible to carry out a scientifically credible analysis of contaminants trends across ecozones+.
Given public concerns regarding environmental pollution arising from the emission of contaminants from human activities, it is surprising that relevant data for assessing trends in substances of concern in river and lake ecosystems are almost completely lacking beyond the Great Lakes region (which is itself covered in a separate Technical Ecozone+ Report). This situation is clearly illustrated for a region where contaminants are considered to be an important ongoing threat to freshwater ecosystems: the Canadian Arctic. In an authoritative review of existing data on contaminants in this area, Braune et al. (1999) state unequivocally that:
"Reviews of contaminant data in freshwater fish from Arctic and sub-Arctic Canada available to 1991 (Muir et al., 1990; Lockhart et al., 1992) indicated that information on the levels and geographic variation of OCs, PAHs and heavy metals was limited while data on temporal trends were non-existent."
The limited number of studies carried out on contaminants in the Canadian Arctic have tended to focus on marine ecosystems (for example, Muir and Norstrom, 2000). Where trend data in freshwater ecosystems are reported, they tend to be locally focused, consist of relatively few sequential observations, and relate to the very recent past (for example, Michelutti et al., 2009). For example, in a research synopsis produced by the Northern Contaminants Program (2008), trends were observed in certain groups of persistent organic pollutants (POPs): HCH, PCBs, toxaphene, and DDT levels in fish tissue were generally seen to be declining across sites studied, whereas mercury trends in fish tissue showed a more complex pattern, with significant increases being observed for some species and locations (for example, lake trout (Salvelinus namaycush) in Great Slave Lake), and no change being reported for species in other areas (for example, charr in lakes in Qausuittuq and Quttinirpaaq). This pattern of spot measurements, patchily distributed and relying on opportunistic sampling as part of short-term local or regional initiatives, has resulted in the current situation, where for much of Canada, time series data on contaminants in freshwater ecosystems are absent. Despite a lack of temporal trend information, the appearance and persistence of bioaccumulative, persistent organic pollutants in remote areas such as the Arctic, which were originally emitted in the more developed southern parts of the North American continent, is a newly emerging trend. This phenomenon is a direct result of global fractionation, a process which was not fully recognised until recently (Wania and Mackay, 1993), and whose implications for transport of a host of substances from industrialised regions to more remote regions is still not completely understood.
Results from the 2008 Canadian Environmental Sustainability Indicators report demonstrated that phosphorus water quality guideline limits were frequently exceeded at 125 of the 369 (34%) monitoring sites (Environment Canada, 2009b). Similarly, the percentages of sites exceeding guidelines in 2002–2004 and 2003–2005 were 38 and 37% respectively (Environment Canada, 2006a; Environment Canada, 2007). In part to evaluate these frequent exceedences, Environment Canada (2011) recently completed a national report exploring trends from 1990 to 2006 in phosphorus and nitrogen in lake and river systems across Canada. Trend analyses of data between 1990 and 2006 demonstrated that 39 of the 77 monitoring sites showed no change in phosphorus levels, 22 showed significant decreasing trends, while 16 showed increasing trends (Figure 29) (Environment Canada, 2011).
Source: Environment Canada (2011)
Long Description for Figure 30
This bar graph shows the following information:
|Major Ocean |
|Pacific Ocean (n=17)||6||9||2|
|Arctic Ocean (n=12)||2||7||3|
|Hudson Bay (n=18)||3||11||4|
|Atlantic Ocean (n=30)||11||12||7|
Glozier et al. (2004) quantified long-term trends in water quality in Banff and Jasper National Parks to assess the effectiveness of sewage treatment plants. Their report applied non‑parametric seasonal Mann-Kendall analysis to assess trends in phosphorus concentrations at five monitoring locations on the Bow, North Saskatchewan, and Athabasca rivers. Results from the first report (Glozier et al., 2004) showed improvements in concentrations of nutrient and bacteriological parameters were observed at downstream sites, particularly in the lower Bow River for the period since 1989. These improvements are largely related to the upgrade of the sewage treatment facility in Banff. Glozier (Glozier, 2009, pers. comm.) reported the results of a follow-up analysis to assess the effectiveness of an upgrade in all three municipalities to tertiary treatment with phosphorus removal. Trend analyses showed that the new facility dramatically reduced phosphorus concentrations in the Bow and Athabasca rivers with median concentrations restored to levels similar to upstream, naturally occurring concentrations (Figure 31). Thus, management practices have dramatically improved water chemistry in these rivers. With continued monitoring, the effects of improved water quality on aquatic communities can be observed.
Concerns about acidification of surface waters arising from atmospheric release of sulphur dioxide (SO2) and nitrogen oxides (NOx) have been prevalent since the 1970s, when scientists first observed declining pH levels, particularly in southeastern Canada (Jeffries et al., 2003a). From 1980 to 2006, SO2 emissions in Canada and the U.S. declined by about 45% and NOx emissions declined by about 19% (Canada-United States, 2008)(Figure 32), due in part to declines in calcium which are also related to acid deposition (Canada-United States, 2008). Declines in calcium also threaten keystone zooplankton species (Jeziorski et al., 2008).Encouraging biological improvements have been seen in some locations (Snucins, 2003; Snucins and Gunn, 2003; Weeber et al., 2005; Environment Canada, 2005; Aurora Trout Recovery Team, 2006; Yan et al., 2008b). Even with chemical recovery, however, biological communities remain altered from their pre-acidification state because many factors beyond acidity influence biological recovery (Yan et al., 2008a; Yan et al., 2008b). The widespread devastation arising from deposition of pollutants carried by atmospheric transport (see also the example of contaminants) presents significant challenges beyond simple emission reduction targets, which challenge our knowledge of ecosystem recolonization and the re-establishment of ecosystem services.
Ecosystems have different sensitivities to acid depending upon their geology and soils. Thus the maximum level of acid deposition that terrain can withstand without harming ecological integrity, called the “critical load”, differs across ecosystems (Figure 33) (Jeffries and Ouimet, 2005). Acid-sensitive terrain is generally underlain by slightly soluble bedrock and overlain by thin, glacially derived soils (National Atlas of Canada, 1991) and has less buffering capacity.
Critical loads can be exceeded either when extremely sensitive terrain receives low levels of acid deposition or when less-sensitive terrain receives high levels of acid deposition. Figure 34 shows where critical loads have been exceeded in the Boreal Shield Ecozone+.
Despite having the lowest rates of acid deposition in eastern North America, the Atlantic Maritime Ecozone+ has some of the most acidic waters due to the poor buffering ability of the terrain (Clair et al., 2004; Clair et al., 2007). Since the 1980s, there has been no measurable recovery in pH despite declines in sulphur dioxide emissions. This has resulted in the most heavily impacted fish habitat in North America (Figure 35) (Clair et al., 2007). Atlantic salmon are highly sensitive to acidity, and by 1996, 14 runs in coastal Nova Scotia were extinct because of water acidity, 20 were severely impacted, and a further 15 were lightly impacted (Watt et al., 2000). Recovery of water chemistry and ecology is expected to take several more decades in Nova Scotia than in other parts of Canada (Watt et al., 2000; Clair et al., 2004; Clair et al., 2007).
While the acidification of lakes has largely been seen as an issue for the Boreal Shield and Atlantic Maritime ecozones+, concerns are being voiced about the potential vulnerability of areas in western Canada. In particular, the potential for critical loads to be exceeded in northwest Saskatchewan is a concern due to the high degree of acid sensitivity of many of the lakes in this area (68% of 259 lakes assessed in 2007/2008) and its location downwind of acidifying emissions from oil and gas developments (Scott et al., 2010) . Similarly, transportation-related sulphur emissions in southwest British Columbia are an emerging issue, with terrestrial critical loads exceeded in 32% of the Georgia Basin in 2005/2006 (Nasr et al., 2010).
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